Body Armor of Ceramic Ball Embedded Polymer

ABSTRACT

A body armor composite material is provided to protect a wearer from small-arms projectiles. The material includes a flexible liner, a polymer binder disposed on the liner, and ceramic balls embedded in the binder. The flexible liner conforms to a portion of the wearer and elastically deforms in response to application of mechanical force.

CROSS REFERENCE TO RELATED APPLICATION

The invention is a Continuation-in-Part, claims priority to and incorporates by reference in its entirety U.S. patent application Ser. No. 15/284,650 filed Oct. 4, 2016, which is a Continuation, claims priority to and incorporates by reference in its entirety U.S. patent application Ser. No. 13/506,376 filed Mar. 9, 2012, published as Application Publication 2012/0312150 and assigned Navy Case 101504. That application, pursuant to 35 U.S.C. § 119, claimed the benefit of priority from provisional application 61/632,734, with a filing date of Jan. 9, 2012 for that non-provisional application, and was a Continuation-in-Part, claims priority to and incorporated by reference in its entirety U.S. patent application Ser. No. 11/157,751 filed Jun. 21, 2005, issued as U.S. Pat. No. 8,220,378 and assigned Navy Case 97280.

STATEMENT OF GOVERNMENT INTEREST

The invention described was made in the performance of official duties by one or more employees of the Department of the Navy, and thus, the invention herein may be manufactured, used or licensed by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND

The invention relates generally to body armor for personnel subject to small-arms fire, such as soldiers and marines in combat as well as law enforcement personnel. In particular, the invention relates to flexible material for protecting personnel from bullet and related projectiles using ceramic balls embedded in polymer.

Military personnel have required protection from enemy weapons for at least four millennia. The advent of kinetic projectiles propelled by chemically produced gas discharge, such as from firearms in the past few centuries, substantially increased kinetic energy transfer to the target's body, thereby raising the risk of mortal injury. Conventional armor has typically focused on either high tensile strength fibrous weave or rigid plates. The former lacks protection from sharp ogive projectiles at high-velocity impact, and the latter constrains motion by inertial weight to carry and by constraints on body movement. In addition the rigid plates have minimal multi-hit capability.

SUMMARY

Conventional personnel armor yield disadvantages addressed by various exemplary embodiments of the present invention. In particular, various exemplary embodiments provide body armor composite material to protect a wearer from small-arms projectiles. The material includes a flexible liner, a polymer binder disposed on the liner, and ceramic solids embedded in the binder. The flexible liner conforms to a portion of the wearer and elastically deforms in response to application of mechanical force.

In various embodiments, the binder can be a foam of polyurea or polyurethane. The solids can be spheres arranged in a single-layer pattern substantially parallel to liner. Other various embodiments alternatively or additionally provide for the ceramic being a metal oxide, nitride or carbide. The liner can be a weave of aramid fibers or alternatively of ultra-high-molecular-weight polyethylene fibers.

BRIEF DESCRIPTION OF THE DRAWINGS

These and various other features and aspects of various exemplary embodiments will be readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings, in which like or similar numbers are used throughout, and in which:

FIG. 1 is elevation and plan views of an armor portion;

FIG. 2 is an elevation view of the portion under stress;

FIG. 3 is a plan view of an ESAPI for large geometry;

FIG. 4 is a tabular view of AD90 test results;

FIG. 5 is a perspective view of arranged ceramic balls;

FIG. 6 is a perspective view of the reverse side of foam backing;

FIG. 7 is a perspective view of tests with various backing;

FIG. 8 is a perspective view of an ESAPI with ceramic spheres;

FIG. 9 is a perspective view of test results;

FIG. 10 is a perspective view of test results;

FIG. 11 is a perspective view of test results;

FIG. 12 is a tabular view of test parameters;

FIG. 13 is a tabular view of test results; and

FIG. 14 is a perspective view of test results.

DETAILED DESCRIPTION

In the following detailed description of exemplary embodiments of the invention, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific exemplary embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized, and logical, mechanical, and other changes may be made without departing from the spirit or scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims.

Conventional body armor teaches, for example, molded ceramic tiles disposed in armor pockets contoured to the body geometry where the tile can be disposed. Each tile forms a small-arms protective insert (SAPI) ballistic plate to protect the wearer from small caliber projectile weapons. This conventional configuration suffers from limited flexibility, tile interface vulnerabilities and lack of multi-hit capability. As a large fixed tile, the SAPI plate restricts movement of the soldier, and after an impact the plate experiences large damage areas leaving vulnerabilities to a second impact in a nearby area. Typically there are four tiles placed at locations both front and back as well as left and right sides. This leaves unprotected areas in the gaps between the plates.

Using the exemplary ceramic ball concept, a continuous mesh of the ceramic balls avoids such gap vulnerabilities by being disposed throughout the protected areas by absorption and deflection of kinetic energy from the striking projectile. Recent tests have demonstrated that performance characteristic even when impacts are performed within “gaps” between balls, minimizing the performance difference between striking in the gaps and direct impact to the sphere. Exemplary embodiments of personnel armor can be designed to specified performance levels at https://www.ncjrs.gov/pdffiles1/nij/223054.pdf by the National Institute of Justice (NIJ). Through varying both ceramic ball diameter and spall liner thickness, various levels can be achieved, with higher NIJ levels requiring more material than lower levels.

Conventional body armor protection incorporates boron carbide (B₄C) ceramic SAPI plates backed by a spall liner of Kevlar® or ultra-high molecular weight polyethylene (UHMWPE). Example conventional body armor configurations include the Outer Tactical Vest (OW) used by the U.S. Army, and the Modular Tactical Vest (MTV) used by the U.S. Marine Corps. These use an embedded spall liner and large pockets in which to insert SAPI plates in the front, back and sides of the MTV to protect key organs. Such a design is comparatively bulky and heavy, so as to limit flexibility and contribute to fatigue of the wearer. Additionally, exemplary SAPI plates cost between $350 and $600 each, so the vests can be expensive. Further, the conventional SAPI plates lack multi-impact protection.

FIG. 1 shows an exemplary armor portion in an elevation view 100 and a plan view 110. A cross-section 120 of the armor portion reveals a laminate structure that includes a flexible substrate 130 and a flexible polymer binder 140 that contains ceramic spheres 150. The substrate 130 can constitute a flexible spall liner to conform to a portion of the wearer to be protected. The binder 140 can constitute a light-weight flexible filler material. The spheres 150 can be produced from various metal carbide, nitride or oxide compounds. In the elevation view 100, the structure shows the binder 140 facing a front surface 160, and the substrate 130 facing a rear surface 170 adjacent to a body portion of the wearer. In the plan view 110, the arrangement of the spheres 150 shows them to share a common plane and be patterned so that six neighboring spheres flank each non-edge counterpart in a hexagonal close packed (HCP) geometric arrangement 180 substantially parallel to the substrate 130. A cover fabric for camouflage or decorative purpose can be overlaid to obscure the binder 140 and the spheres 150 from visual observation.

FIG. 2 shows an elevation view 200 of the section elastically deforming under stress. Forces 210 cause the structure to flex such that the cross-section 120 bows in response, particularly in view of the mechanical properties of the substrate 130. As shown, the rear surface 170 bends to form a convex profile in cross-section, whereas the front surface 160 bends to form a concave profile.

Parent U.S. Pat. No. 8,220,378 illustrates, in parent FIGS. 2A and 2B, a composite armor panel 42 for mounting to a vehicle door 40. The panel 42 includes a metal substrate 46 overlaid with a polymer layer 50 in which a layer 44 of ceramic spheres 48 are disposed. Techniques for producing these laminate structures are described with parent FIGS. 3A through 4C. Further, parent FIGS. 5A through 5C illustrate the damage mitigation effects to protect the body behind the panel by kinetic absorption through the ceramic spheres 136.

By contrast, various exemplary embodiments for the present invention provide for protection to be worn on a human body, rather than mounted to a vehicle, and thus requiring greater flexibility and lighter weight than for the parent application. In particular, the substrate 130 and the binder 140 constitute less dense and more flexible material than disclosed in the parent application. For example, the substrate 130 can be composed of Kevlar® or UHMWPE, with or without adhesives.

The exemplary structure provides a light-weight, flexible, multi-hit-capable body armor material. Within the exemplary design, the ceramic spheres 150 are encapsulated within the light-weight flexible polymer binder 140 to provide flexibility reinforced by a spall liner that constitutes the substrate 130. The solution can be incorporated to all applications related to protecting the torso and groin regions of the wearer. Preferred applications include vest and an outer garment to protect the groin region.

Various exemplary embodiments provide the ceramic spheres 150 to include diameters ⅜″ (0.375 inch) up to ¾″ (0.75 inch) and form an encapsulated layer having thicknesses that substantially correspond to the sphere's diameters. The ceramic components form a spherical shape, although alternate substantially symmetrical solids, such as the octahedron, dodecahedron and icosahadron can be used without departing from the scope of the invention. Complete encapsulation with overall layer thickness between ⅜″ and ¾″.

Candidate ceramic materials include aluminum oxide (alumina or Al₂O₃) of all chemical purity varieties, silicon carbide (SiC), and boron carbide (B₄C), the latter two being both sintered and hot pressed. Alternate materials include boron nitride (BN), silicon nitride (Si₃N₄), and zirconium oxide (zirconia or ZrO₂). Preferably, the ceramic spheres 150 are at least 90% alumina. Regardless of the ceramic material selected, a high hardness and compression strength is preferable. A Vickers Hardness number of at least 15 is suitable, and a Vickers Hardness number of at least 30 is preferable. The HCP pattern 180 exhibits a high degree of symmetry. The ceramic spheres 150 are uniform and oriented in the direction of anticipated impact.

The ceramic spheres 150 are encapsulated in a single layer within the lightweight flexible polymer binder 140 in the HCP pattern 180. The polymer binder 140 enables flexible motion of the encapsulated ceramic ball matrix, which is backed by the spall liner substrate 130 and affixed thereto by an optional adhesive. Additionally, the ceramic spheres 150 can be tightly wrapped in a high strength polymer thread, similar to a ball of yarn prior to being embedded in the encapsulating polymer binder 140. This thread-wrapping measure enables the spheres 150 to be held in compression and provides additional integrity to the spheres 150 when subject to kinetic impact. Such threads can be composed of a light metal weave or high tensile strength fiber, such as UHMWPE, or an aromatic polyamide for example, the best known being Kevlar® from duPont of Wilmington, Del.

The polymer layer 140 may comprise preferably light-weight flexible polyurea foam. Related materials can include polyurethanes, polyureas, rubbers or combinations of elastomeric materials incorporating urethanes, polyureas or hybrids thereof such as acrylics and methacrylates. Preferably, the polymer thermosets and demonstrates medium to high elongation (e.g., 50% to 100%), a medium to high modulus, and high tensile strength, such as a polyurea, notable for high durability.

Alternatively, the polymer layer 140 may comprise polyurethane, which has a lower density than polyurea (for reduced weight at the cost of decreased durability). Further material differences between polyurea and polyurethane is available in a report “Polyurea Elastomer Technology” by Dudley J. Primeaux II from Primeaux Associates LLC in Elgin, Tex., available in http://www.hansonco.net/PUAHistChemFormulate%20by%20Dudley.pdf as a report.

In another embodiment, the polyurea elastomers may be derived from hybridized isocyanate/resin components. The isocyanate may be aromatic or aliphatic in nature. Additionally, the isocyanate may be a monomer, a polymer, or any variant reaction of isocyanates, quasi-prepolymer or a prepolymer.

The prepolymer, or quasi-prepolymer, may comprise an amine-terminated polymer resin, or a hydroxyl terminated polymer resin. More specifically, the resin blend utilized with the prepolymer or quasi-prepolymer may comprise amine-terminated polymer resins, and/or terminated chain extenders. The resin blend may also contain additives, or non-primary components. For example, the additives may serve cosmetic functions, weight reduction functions, or provide fire-retardant characteristics. By way of further example, these additives may contain hydroxyls, such as pre-dispersed pigments in a polyol carrier. By way of another example, a polyurethane/polyurea hybrid elastomer may be utilized which is the reaction product of an isocyanate component and a resin blend component.

The isocyanate may be aromatic or aliphatic in nature. Further, the isocyanate may be a monomer, a polymer, or any variant reaction of isocyanates, quasi-prepolymers or prepolymers. The prepolymer, or quasi-prepolymer, may comprise an amine-terminated polymer resin, or a hydroxyl-terminated polymer resin. Additionally, the resin blend may comprise blends of amine-terminated and/or hydroxyl-terminated polymer resins, and/or amine-terminated and/or hydroxyl-terminated chain extenders.

In one embodiment, the resin blend contains blends of amine-terminated and hydroxyl-terminated moieties. The resin blend may also contain additives, non-primary components or catalysts. As a further example, a polyurethane elastomer may be the reaction product of an isocyanate component and a resin blend component. In another embodiment, the polyurethane elastomer is the reaction product of hybridized isocyanate and resins.

The isocyanate component may be aromatic or aliphatic in nature. Further, the isocyanate component may be a monomer, polymer, or any variant reaction of isocyanates, quasi-prepolymer, or a prepolymer. The prepolymer, or quasi-prepolymer, may comprise hydroxyl-terminated polymer resins. The resin blend may be composed of hydroxyl-terminated polymer resins, being -diol, -triol or multi-hydroxyl polyols, and/or aromatic or aliphatic hydroxyl-terminated chain extenders. The resin blend may also contain additives, non-primary components, or catalysts.

Both the adhesive and spall liner substrate 130 must be of equal or greater compliancy as the ceramic ball matrix. Compliancy may be obtained through reduced bonding resins or reduced heat and pressure used to combine the multi-layers that form the substrate 130 as the spall liner. Candidate materials include both aramid and UHMWPE fibers such as Dyneema® fiber (or yarn) by Royal DSM N.V. of Amsterdam, the Netherlands, and Spectra® yarn of Honeywell in Morristown, N.J. These fibers can be woven to establish a weave that conforms to the wearer, and thereby serve as the flexible substrate 130.

Returning to FIG. 1, the configuration and arrangement of the composite ceramic body armor system can be characterized as encapsulated ball matrix serving as the “strike face” along the front surface 160. The ceramic spheres 150 arranged in a patterned layer within the polymer binder 140 constitute the encapsulated ball matrix. A flexible adhesion is provided between that encapsulated ball matrix and the spall liner substrate 130. Additionally the entire body armor system may be wrapped in a fabric material to provide: protection of armor system, uniformity with existing clothing and camouflage options. Performance gains from this feature include: increased flexibility, multi-hit capability, lower cost and lighter weight (as compared to conventional armor for equal performance characteristics).

Damage areas after an impact tend to be minimal where typically only two or three ceramic spheres 150 are removed. The application of the ceramic ball body armor can be integrated to primarily protect the torso and groin area due not only to damage vulnerability but also to target size compared to the head and appendages, such as arms and legs.

The exemplary garment form can be described primarily of a vest, but could include an outer garment protecting the groin area. Customized designs can be incorporated based on threat requirements. Increased threats would need to include larger ceramic balls and thicker spall liners. The protection system would be worn similar to the conventional existing SAPI system as an over garment in tactical conditions. In 2008, the United States Army stated that the SAPI plate system was not a final state for body armor protection. Future requirements would include increased flexibility and lighter weight. The ceramic ball armor disclosed in exemplary embodiments addresses both issues.

Production of the composite body armor include spraying polymer binder 140 onto the substrate 130, such as with Gusmer® spray equipment from Gusmer-Decker (acquired by Graco) of North Canton, Ohio, and potting the spheres 150 in the HCP pattern 180 into the sprayed polymer prior to its curing. The polymer surrounding the ceramic balls must enable flexible motion of the encapsulated ceramic ball matrix. Other techniques for producing such body armor can be envisioned by artisans of ordinary skill without departing from the scope of the invention.

In exemplary embodiments, the encapsulated ceramic ball serves as the “strike face” of the body armor system. Flexible adhesion is provided between the encapsulated ball system and the spall liner. Additionally the entire body armor system may be wrapped in a fabric material to provide: protection of armor system, uniformity with existing clothing and camouflage options. Benefits from this design include: increased flexibility, multi-hit capability, lower cost and lighter weight (as compared to conventional armor for comparable performance characteristics).

Further design and evaluation provide additional information in relation to Enhanced Small Arms Protective Insert (ESAPI) used for body armor in the United States Armed Forces. FIG. 3 shows a plan diagram view 300 of a large ESAPI panel 310 that forms a chamfered rectangle. The overall mass of the large panel 310 is 2.85 kg (6.8 lb) length of the panel 310 is 13¼″×10⅛″.

Calculation of ESAPI panel densities based on ballistic performance can be provided as follows: Application of SiC spheres with 97% theoretical maximum density, 0.97 (fill)×3.21 g/cm³ provides 3.11 g/cm³. The diameter of the SiC spheres is 7/16″, with double the corresponding number of satellite spheres 3/16″ uniformly distributed. The encapsulating material (PU foam) density is 0.18 g/cm³. The number of balls along the horizontal would be 27.4 spheres per foot, while along the vertical would be 30.6 spheres per foot due to higher stacking efficiency compared to horizontal. This places the total number of 7/16″ spheres at 839 spheres per square foot. Double this packing density provides the number of 3/16″ spheres at 1678 spheres per square foot.

The corresponding volume of a 7/16″ sphere would be 1.33×π×(0.556)³ cm³=0.718 cm³ and a mass of 2.23 g individually and 839×2.23 g=1.871 kg for their total. The corresponding volume of a 3/16″ sphere would be 1.33×π×(0.238)³ cm3=0.056 cm³ and a mass of 0.175 g individually and 1678×0.175 g=0.294 kg for their total. The combination of 7/16″ and 3/16″ spheres is then 1.871 kg+0.294 kg=2.165 kg. The foam at ½″ thickness for the panel 310 would have a volume 1.27 cm×30.48 cm×30.48 cm=472 cm³. With a density of 0.18 g/cm³, the mass of the panel 310 is 0.085 kg. The combined mass of the panel with spheres is 2.165 kg+0.085 kg=2.25 kg=4.96 lb. This enables the exemplary concept of foam ESAPI with SiC spheres to reduce the mass of a large panel by 21 percent from the conventional version. Note that alternate ceramics include alumina Al₂O₃ and silicon nitride Si₃N₄, along with alternate sphere diameters of 9/16″, ½″, 7/16″ 10 mm and ⅜″.

FIG. 4 shows a tabular view 400 of NIJ Level IV body armor test results for four tests. The first column 410 denotes the shot number. The second column 415 identifies the front target. The third and fourth columns 420 and 425 identify the backing material and mass in grams. The fifth and sixth columns 430 and 435 denote the projectile and propellant mass. The seventh and eighth columns 440 and 445 respectively identify first and second velocities in feet-per-second. The ninth column 450 identifies the pen. The tenth column 455 provides the unpenetrated material mass in grams.

FIG. 5 shows a perspective view 500 of a target of arrayed spheres. The view 500 shows ½″ AD90 spheres 510 on the bottom level interspersed by 7/32″ AD90 backing spheres 520 on top.

FIG. 6 shows a perspective view 600 of a reverse side 610 of an SB71 from a ballistic impact at 100 feet-per-second above the required velocity. FIG. 7 shows a perspective view 700 of the target of AD90 spheres from view 500, with four separate backing systems. All four shots demonstrate complete arrest of the projectile after striking the target, with the impact position revealing minimal dispersion. FIG. 8 shows a perspective view 800 of an exemplary ESAPI 610 with spheres 510 disposed thereon in an HCP pattern 180.

FIG. 9 shows a perspective view 900 of eight test results that successfully stopped armor piercing incendiary (API) bullets. Target areal densities varied from 5.16 lb/ft² to 7.54 lb/ft². Comparison to conventional steel plate body armor (10.26 lb/ft²) indicates ceramic ball armor between 50 percent and 73 percent lighter.

FIG. 10 shows a perspective view 1000 of fifteen test results that stopped API bullets. Target areal densities varied from 5.35 lb/ft² to 7.22 lb/ft². The comparison to conventional steel showed similar results to view 900. FIG. 11 shows a perspective view 1100 of eleven exemplary targets having ⅜″ diameter spheres with areal densities varied from 5.5 lb/ft² to 6.7 lb/ft², including multiple strikes. These images are shown as images 1110, 1120, 1130 and 1140.

FIG. 12 shows a tabular view 1200 of test parameters for clay calibration. This was set for an average of 0.685″ (with 2.5″ diameter steel sphere dropped from two meters), with a required depth of 0.787″±0.12″. The first column 1210 identifies the shot number. The second column 1220 identifies the projectile (all being 7.62×39 BZ API rounds). The third column 1230 indicates the velocity in feet-per-second. The fourth column 1240 denotes the pen. The fifth column 1250 denotes the clay depth. FIG. 13 shows a tabular view 1300 of the clay calibration empirical results. The first, second and third columns 1210, 1220 and 1230 identify the shot number, projectile and velocity corresponding to view 1200. The fourth and fifth columns 1310 and 1320 identify the spherical diameter and ceramic material. The fifth and sixth columns 1330 and 1340 identify the backing material mass in grams and backing material. The seventh column 1350 identifies the ceramic and foam areal density in pounds-per-square-foot. The eighth column 1360 denotes the backing material areal density in pounds-per-square-foot. The ninth column 1370 provides the total areal density in pounds-per-square-foot.

FIG. 14 shows perspective views 1400 of four tests showing defeat of .30 caliber M2AP rounds with 1.75″ separation at 100 feet-per-second velocity above muzzle velocity. The first image 1410 shows a substrate 1420 on obverse face with a plate 1430 in plan view that includes ceramic spheres. The second image 1440 shows the plate 1430 in plan view after damaged from impact. The third image 1450 shows the plate 1430 in elevation view. The fourth image 1460 shows the reverse side of the substrate 1420.

While certain features of the embodiments of the invention have been illustrated as described herein, many modifications, substitutions, changes and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the embodiments. 

1. A body armor composite material for flexibly conforming to and protecting a wearer from small-arms projectiles and shrapnel, said material comprising: a flexible liner that conforms to a portion of the wearer and elastically deforms in response to application of mechanical force; a binder of polyurea foam disposed on said flexible liner; and a plurality of ceramic balls embedded within said binder, wherein said plurality is arranged in a hexagonal close-packed single-layer pattern substantially parallel to said liner such that each non-edge ball has six neighboring balls in said pattern.
 2. The body armor according to claim 1, wherein each ceramic ball of said plurality is between ⅜″ and ¾″ in diameter.
 3. The body armor according to claim 1, wherein said each ceramic ball is composed of at least one of aluminum oxide (Al₂O₃), silicon carbide (SiC), boron carbide (B₄C), boron nitride (BN), silicon nitride (Si₃N₄), and zirconium oxide (ZrO₂).
 4. The body armor according to claim 1, wherein said each ceramic ball is composed substantially of aluminum oxide (Al₂O₃).
 5. The body armor according to claim 1, wherein said binder is between ⅜″ and ¾″ in thickness.
 6. The body armor according to claim 1, wherein said liner comprises a weave of one of aramid fibers and ultra-high-molecular-weight polyethylene (UHMWPE) fibers.
 7. The body armor according to claim 1, wherein a polymer thread wraps said each ceramic ball, said thread being composed of at least one of aramid fibers, UHMWPE fibers and metal.
 8. The body armor according to claim 1, wherein said plurality of ceramic balls includes inner and outer facing hexagonal layers, with inner ceramic balls being smaller than outer ceramic balls and each inner ceramic ball being disposed at a joint between adjacent outer ceramic balls.
 9. A small-arms protective insert (SAPI) ballistic panel for disposal in a body armor pocket for flexibly conforming to and protecting a wearer from small-arms projectiles and shrapnel, said plate comprising: a flexible liner that conforms to a portion of the wearer and elastically deforms in response to application of mechanical force; a binder of polyurea foam disposed on said flexible liner; and a plurality of ceramic balls embedded within said binder, wherein said plurality is arranged in a hexagonal close-packed single-layer pattern substantially parallel to said liner such that each non-edge ball has six neighboring balls in said pattern.
 10. The SAPI panel according to claim 9, wherein each ceramic ball of said plurality is between ⅜″ and ¾″ in diameter.
 11. The SAPI panel according to claim 9, wherein said each ceramic ball is composed of at least one of aluminum oxide (Al₂O₃), silicon carbide (SiC), boron carbide (B₄C), boron nitride (BN), silicon nitride (Si₃N₄), and zirconium oxide (ZrO₂).
 12. The SAPI panel according to claim 9, wherein said each ceramic ball is composed substantially of aluminum oxide (Al₂O₃).
 13. The SAPI panel according to claim 9, wherein said binder is between ⅜″ and ¾″ in thickness.
 14. The SAPI panel according to claim 9, wherein said liner comprises a weave of one of aramid fibers and ultra-high-molecular-weight polyethylene (UHMWPE) fibers.
 15. The SAPI panel according to claim 9, wherein a polymer thread wraps said each ceramic ball, said thread being composed of at least one of aramid fibers, UHMWPE fibers and metal.
 16. The SAPI panel according to claim 9, wherein said plurality of ceramic balls includes inner and outer facing hexagonal layers, with inner ceramic balls being smaller than outer ceramic balls and each inner ceramic ball being disposed at a joint between adjacent outer ceramic balls. 